Ahabaev, B A

Artamonov, S A

Skorobogatov, P K

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AbstractThe dependence of p-i-n diode ionizing current amplitudevs dose rate is defined using two-dimensional softwaresimulation. It is shown that analyzed dependence becomesnonlinear beginning with relatively low dose rates near 107rad(Si)/s. This effect is connected with the modulation of p-i-n diode intrinsic region by irradiation. As a result thedistribution of electric field becomes non-uniform that leadsto decrease of excess carriers collection. The ionizing currentpulse form becomes more prolonged because of delayedcomponent contribution. It is necessary to take into accountwhen p-i-n diode is used as dose rate dosimeter.I. INTRODUCTIONThe p-i-n diodes are widely used for the measurements ofionizing radiation dose rates. The high electric field in itsintrinsic region provides the full and fast excess carrierscollection. As a result the ionizing current pulse waveformrepeats the ionization pulse with the accuracy of severalnanoseconds.Possible nonlinear ionization effects may disturb thebehavior of p-i-n diode at high dose rates. Here we presentthe results of a recent study of typical p-i-n diode usingnumerical simulation and pulsed laser simulator with 1.06µm wavelength as a radiation source.II. P-I-N DIODE STUDYThe typical p-i-n diode with 380 micrometers intrinsicregion thick at 300 V reverse bias was investigated. P-i-ndiode cross-section is shown in Fig. 1. Sensitive area size is2.3x2.3 mm. The p+ and n+ regions of diode are doped up to1019 cm–3.To investigate the p-i-n diode possibilities at high doserates the original software simulator “DIODE-2D” [1] wasused. The “DIODE-2D” is the fundamental system ofequations two-dimensional solver. It takes into accountcarrier generation, recombination and transport, opticaleffects, carrier’s lifetime and mobility dependencies on excesscarriers and doping impurity concentrations.The calculated p-i-n diode ionizing current pulseamplitude vs dose rate and laser intensity dependency underreverse bias 300 V is presented in Fig. 2. The radiation pulsewaveform was taken “Gaussian” with 11 ns duration. Onecan see that the direct proportionality between current pulseamplitude and dose rate (laser intensity) takes place only atrelatively low dose rates (up to 107 rad(Si)/s). The ionizationdistribution nonuniformity connected with laser radiationattenuation does not affect the dependence.Figure 1: P-i-n diode cross-sectionFigure 2: P-i-n diode ionizing current pulse amplitude vs dose rateand laser intensity dependencyThe reason of non-linearity is connected with themodulation of p-i-n diode intrinsic region by excess carriers.Because of low level of initial carriers concentration theThe Nonlinear Behavior of P-I-N Diode in High Intense Radiation FieldsSkorobogatov P.K., Artamonov A.S., Ahabaev B.A.Specialized Electronic Systems, Kashirskoe shosse, 31, 115409, Moscow, Russiapkskor@aha.ru)modulation takes place at relatively low dose rates. As aresult of modulation the distribution of electric field in theintrinsic region becomes non-uniform that leads to decreaseof excess carriers collection. This proposal is confirmed byresults of potential distribution calculations presented in Fig.3.Figure 3: Potential vs distance distributions at time 11 ns fordifferent maximum dose rates: initial (1), 107 (2), 108 (3), 109 (4),1010 (5), 1011 (6) and 1012 (7) rad(Si)/sThe behavior of p-i-n diode becomes similar to that ofordinary p-n junction with prompt and delayed componentsof ionizing current. The prompt component repeats the doserate waveform. The delayed component is connected with theexcess carriers collection from regions with low electricfields. As a result the ionizing current pulse form becomesmore prolonged and dose not repeat the dose rate waveform.Figure 4: Normalized calculated ionizing current pulse waveformsfor different maximum dose rates: 107 (1), 108 (2), 109 (3) and 1011(4) rad(Si)/sFig. 4 depicts the normalized calculated ionizing currentpulse waveforms for different maximum dose rates. Atrelatively low dose rate the current pulse waveform repeatsthe appropriate radiation pulse waveform. At high dose rateswe see the delayed components.The non-linear character of behavior and prolongedreaction must be taken into account when p-i-n diode is usedas dose rate dosimeter.III. NUMERICAL TO EXPERIMENTAL COMPARATIVERESULTSThe numerical results were confirmed by experimentalmeasurement of p-i-n diode ionizing reaction in wide rangeof ionizing radiation dose rates.Pulsed laser simulator "RADON-5E" with 1.06 µmwavelength and 11 ns pulse width was used in theexperiments as a radiation source. The laser pulse maximumintensity was varied from 6·102 up to 2.1·106 W/cm2 withlaser spot size covering the entire chip. It provides in siliconthe equivalent dose rates up to 1012 rad(Si)/s. The p-i-n diodeionizing current transient response was registered with"Tektronix TDS-220" digital oscilloscope.The comparative p-i-n diode ionizing current pulseamplitude vs laser intensity dependencies under reverse bias300 V are presented in Fig. 5.Figure 5: Numerical (line) and experimentally determined (dots) p-i-n diode ionizing current amplitude vs laser intensityOne can see that the experimental results confirm thenon-linear behaviour of p-i-n diode at dose rates above 107rad(Si)/s.As for the distortion of pulse waveform at high dose ratesit was confirmed also. The experimental p-i-n diode currentpulse waveforms are represented in Fig. 6. At dose rate 1,6⋅106 rad(Si)/s the current pulse waveform repeats the radiationone. At dose rate 3,4⋅ 107 rad(Si)/s we can see prolongedbehavior.a)b)Figure 6: P-i-n diode ionizing current waveforms under laser pulseswith 1.6 106 (a) and 3,4 107 (b) rad(Si)/s equivalent dose ratesIV. CONCLUSIONThe simulation and experiments under p-i-n diodestructure have shown that linear dependence between doserate and ionizing current pulse amplitude is valid only atrelatively low dose rates up to 107 rad(Si)/s. In the field ofhigh dose rates this dependence becomes non-linear andionizing current increases more slowly than dose rate. Theionizing current pulse form becomes more prolonged anddose not repeats the dose rate waveform.The non-linear character of behavior and prolongedreaction must be taken into account when p-i-n diode is usedas dose rate dosimeter.IV. REFERENCES[1]. The "DIODE-2D" Software Simulator Manual Guide, SPELS,1995.

The nonlinear behavior of P-I-N diode in high intense radiation fields

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